1. Field of the Invention
The present invention relates to glass compositions for the manufacture of materials intended for use in agriculture field. More specifically, the present invention relates to vitreous products intended for plant nutrition.
2. Discussion of the Background
Glass fibers or glass powders can be used as examples of vitreous products within the sense of the invention.
The term "glass powders" mean any powdery glass material obtained by all known methods of fragmentation. Thus glass, having any shape whatsoever following the pouring operation, can be crushed, ground and sieved to obtain a glass powder.
The glass powder can also be obtained by pouring glass directly into water where the glass is subjected to violent cooling which provokes the appearance of sufficiently strong internal pressures to cause fragmentation of the glass into fine particles. These particles are subsequently dried and sieved to obtain a glass powder.
It is possible to include a very large variety of elements in the glass compositions and the most varied applications can be envisaged. The selection of the compositions generally depends on a compromise between several needs which are frequently contradictory: the cost of the various raw materials, the requirements imposed by the devices for working the manufacturing methods and the desired properties. In the field of agriculture and in particular that of plant nutrition, glass compositions leaving advantageous exchange capability with the medium with which they are in contact, are preferred.
In effect, plants need a large number of mineral elements for their growth. These elements, for the most part, can be included in a glass composition. Depending on the plant's content in each of the elements, they are generally classified in two categories: macroelements or major elements which include N, P, K, S, Ca and Mg; and trace elements or minor elements, which are also indispensable but are present in smaller quantities and which include Fe, Mn, Zn, B, Cu and Mo.
A plant normally draws the necessary elements for its growth from the soil. Not all soils, however, possess properties suitable for satisfactory plant nutrition. Some are too poor or totally lacking in indispensable elements for plant growth. Others effectively contain these elements, but the transfer to the plant does not take place correctly in the amounts necessary for satisfactory growth.
For efficacious transfer of the elements to the plant, the nutritive element must be capable of being soluble in the liquid phase of the culture medium, with only the element in solution being capable of being assimilated by the plant. However, this solubility must also be controlled and take place in proportion corresponding to the absorption needs for the elements in question by the plant, and therefore in proportion with the needs of the plant. If the solubility required is not provided, the effectively liberated elements can be drained-off or even react chemically with the soil, and are not assimilated by the plant.
Means have therefore been developed either for enriching the soil with elements which are indispensable to the plant, or for improving the capability of the plants to assimilate said elements.
The practice of culture out of the soil has also been strongly developed. In accordance with this technique, varied substrates are used which support the roots of the plants and are fed with a nutritive solution which contains the elements necessary for the growth of the plants. The selection of the elements and their proportions in a nutritive solution depends on the needs of the plant. The selection of the type of substrate itself depends on its qualities for facilitating culture. Among all these required qualities, the absence of elements which are toxic to plants, the absence of pathogenic elements, good resistance to degradation and to packing can be cited as being particularly important.
Since the substrate therefore can constitute the sole medium for development of the root system, certain physical characteristics are also required: in particular, these are a good water retention capability, which enables the watering rhythm to be determined; a capability for aerating the root medium, which is conditioned by the density of the substrate. The substrate must also ensure good circulation of the nutritive solution.
Vitreous products such as glass fibers and powders intended to be applied in the field of agriculture are known. For example, U.S. Pat. No. 2,192,939 describes glass fibers packed in the form of a fiber pad arranged on the ground before seeding it. The fibers described in this patent contain elements known for their fertilizing properties, which are easily soluble and are introduced in appropriate quantities for enriching the soil. The glass compositions selected provide, for the most part, phosphorus and potassium. They fulfill a multiple role which is always associated with the soil: enrichment or protection of the soil. The growth of the plants is therefore provided by the combined contribution of the soil and the fiber pad.
From the publication of German Patent DE-AS 1 008 757, glass powders are also known which are obtained by melting of the composition and then sudden cooling in water followed by a drying and sieving operation. These glass powders can be used directly as a nutritive support and render certain nutritive elements directly accessible to the roots. In spite of the presence of one or several nutritive elements in this product, it is supplied with a solution which itself contains one or several nutritive elements. With such a system, the growth is produced by the combined contribution of the support and the nutritive solution.
The present invention has therefore as an object to provide a new vitreous product which can be applied to agriculture and which has improved properties in relation to the known agricultural products. In particularly this invention also has as an object to provide a nutritive medium for the culture of plants outside of the earth, i.e., a medium which combines the functions of nutrition and of support for the root system of the plants.
In this regard, the object of this invention is to simplify the work of the horticulturist. In effect, in the most common operation of a method of culture outside the earth as described above, on a substrate which is agronomically inert, the elements which are essential to the plants are brought by the nutritive solution which must contain them all. However, due to the fact of the multiplicity of the elements, the preparation of such a solution requires a certain number of precautions which take a lot of time. In particular, in order to avoid the formation of precipitates, several solutions must be prepared separately each containing a limited number of elements, and they must be used immediately.
In this regard, one of the objects of the invention is to eliminate the nutritive solution. The previously cited prior art does not eliminate this disadvantage insofar as the use of a more less complex nutritive solution is always provided.